Conventional traction elevator systems include a passenger car, a counterweight, two or more wire cables interconnecting the passenger car and the counterweight, a traction sheave to move the cables and a machine to move the traction sheave. Although this design has proven reliable and cost effective for many years, the wire cables employed in such a system have limited service lives. This limitation is the result of several factors. For example, to enhance friction forces between the cable and the sheave, the wrap angle of the cable is either increased or another possibility is to undercut grooves in the sheave. Both techniques subject the cable to increased wear and/or increased rope pressure. Another limitation associated with traditional steel cables is the need to produce cables of a sufficient diameter to comply with elevator safety codes. The imposed cable diameters require larger sheave diameters, which in turn, require greater torque from the machine used to drive the system.
The greater applied torque combined with pressure imposed by the sheave, subjects conventional elevator cables to great stress, which in turn shortens the service life as a tension member. Engineers under the direction of Otis Elevator, designed an elevator tension member that effectively minimized the various stress forces on the member so as to produce a more durable tension member with a longer service life than conventional cables. To accomplish this goal, the tension member consists of a plurality of individual load carrying cords encased within a common layer of coating that separates the individual cords while at the same time defining an engagement surface for the traction sheave. The coating layer is formed from a polyurethane material extruded onto and through the plurality of cords. The resulting tension member is relatively flat. The flattening out of the tension member minimizes the thickness and maximizes the width of the tension member without sacrificing cross-sectional area or load carrying capacity. As a result, stronger more flexible “belt-like” elevator tension members are produced. Details relating to the manufacture of coated steel elevator tension belts are disclosed in commonly owned U.S. patent application Ser. No. 406,453, now U.S. Pat. No. 6,295,799, the contents of which are herein incorporated in their entirety by reference. This novel tension member shall hereinafter be referred to as a “coated steel belt.” This design distributes the pressure more uniformly throughout the tension member, thus reducing the maximum pressure applied to the tension member as compared to a conventional cable having a similar load capacity. Furthermore, the effective member diameter of the sheave is minimized which in turn reduces the magnitude of the torque needed to drive the sheave which in turn increases the rotational speed. Coated steel belts permit the use of less costly, more compact high speed motors as the driving mechanism of the elevator system.
The traction sheave and one surface of the coated steel belt are complimentary contoured to provide traction and to guide the engagement between the coated steel belt and the sheave. Conventional elevator cables, having no such traction enhancing contouring, need only be individually fed down the elevator shaft for installation. It was discovered that attempts to install the novel coated steel belts using traditional elevator cable installation methods were time consuming and resulted in damage to the belts. Because of its contoured surface, diligent attention was required to ensure proper installation of the coated steel belts so that the contoured surface of the belts came in contact with the surface of the sheave. The coated steel belts have a tendency to twist when fed individually down the elevator shaft. This twisting can damage the belt. Therefore, there exists a need for a new and improved method of installing coated steel belts as tension members in elevator systems without causing twisting of the coated steel belts during installation.